A woman running naked through the jungle is killed by a man-like creature. A ship arrives at Blood Island carrying American pathologist Bill Foster(John Ashley), who is investigating the discovery of green blood; Sheila Willard (Angelique Pettyjohn), who has come to find her father; and Carlos Lopez (Ronaldo Valdez), who wants to get his mother, Mrs. Lopez (Tita Munoz), off the island. The captain of the ship claims that the island is cursed and tells a story of a man they picked up on a raft who bled green blood.Sheila finds her father (Tony Edmunds) to be a hopeless drunk. Carlos' mother doesn't want to leave the island, even though her husband is dead. Dr. Lorca (Ronald Remy) doesn't tell much about Don Ramon Lopez's death. Marla (Alicia Alonzo) drops some hints about Don Ramon, much to the annoyance of Carlos' mother.Dr. Lorca and his assistant Razak (Bruno Punzalan) head into the jungle, looking for something. One night a native with green sores on his body tries to break into the government house but gets away. The next day, Willard goes into the jungle to watch Marla swim. Sheila follows him before she is attacked by a monster who butchers one of the natives. It is revealed that Dr. Lorca has been experimenting on the islanders, including Don Ramon, who was dying of cancer but was turned him into a monster by Lorca's serum.Ramon kills his wife and Dr. Lorca captures Carlos. Marla, who was Don Ramon's lover, leads him to Dr. Lorca, who is apparently killed. A fire breaks out and Lorca's lab explodes. Sheila, her father, Dr. Foster and Carlos return to the ship to leave the island. A hand appears under a tarp, dripping green blood.